Fountain pen



FIG. 1 is a side elevational view of a fountain pen showing our new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a left end elevational view thereof; and

FIG. 5 is a right end elevational view thereof. 

The ornamental design for a fountain pen, substantially as shown and described. 